Eddie Murphy's a good example. His old shit was grade A.
Robin Williams in recent years has been on a turkey spree.
The Matrix. I say this mostly because Laurence Fishburne is awesome, and these movies were hyped like Jesus in digital form. Woodshop "philosophy" propped up by cool effects.
Mel Gibson--Signs. At least the Matrix was pretty obviously going nowhere from the beginning. Signs actually mislead you into believing there was some sort of plot or something holding it together...Until the end, where the only surprise of the endingof this suspense movie is SURPRISE! You wasted 8 bucks to watch a train wreck.
Unbreakable.